Thank you for responding! I've captured some screenshots. Server population was about 70, couldn't find more populated server at morning, when I had time. First one was captured on a fire range for comparison.

OS: Windows 10 (last version)
CPU: Intel I-5 7500 stock
GPU: MSI GTX 970 4GB stock (last driver version, clean install)
RAM: 4x4 Corsair LPX 2400 hz 4 GB (page file size set to automatic).
When I use 'stat unit' console command it shows 15-17 GPU time even on Fire range, however gtx 970 is in recommended system requirements.
When I play on a full server i get 45-70 fps, average 56 with drops to even 30 sometimes and it kills all fun
Also changing everything to low doesn't make any significant performance boost.
I hope things will change in future, because I love this game so much =)